i suggest you try loading the battery kernel module first:
# modprobe battery
if that helps, you can auto-load it on boot by adding a line reading "battery" to /etc/modules.
if it doesn't, you need to recompile the kernel. there's a kernel compilation tutorial
on this site.
The Linux Documentation Project
also maintains a Kernel-HOWTO, but it seems to be offline right now.
When configuring the kernel, you'll find the battery support under Power Management/ACPI/battery